1. Field of the Invention
The invention relates to a hollow profile bar, especially of extruded metal, comprising a tubular wall that is equally thick all around and is provided with salient outer webs, evenly distributed about the outer circumference, which in pairs form undercut casing grooves with side walls, a radial salience of the outer webs from the tubular wall being practically equal to the thickness of said tubular wall.
2. Description of the Prior Art
A hollow profile bar having the aforesaid features is known from DE U 296 15 208. The outer webs are broader at their outer circumference than at their circumference defined by the bottom of the casing grooves, thus forming a corresponding undercut. The degree of undercutting is determined, i.e., rendered minimal, by the fact that the slope lines intersect approximately within the axis of the tube. To make it possible to connect other hollow profile bars, links are used that can subsequently be xe2x80x9cdockedxe2x80x9d at any point on the undercut outer webs. Because of the minimal undercutting of the outer webs, such links extend over a substantial circumference of the hollow profile bar and comprise in particular four coupling saliences, each of which engages in a respective casing groove. One result of this arrangement is uneven loading of the coupling saliences and thus the link; moreover, no more than four links can be used, thereby limiting the number of structures that can be connected to a hollow profile bar in one plane.
It is further known, for example from GB A 1 557 693, to realize sharply undercut outer webs on hollow profile bars having a tubular wall that is equally thick all around. The outer webs are T-shaped or have an anchor-shaped cross section. They form a polygonal outer circumference of the hollow profile bar. Its casing grooves are of large volume, resulting in substantial instabilities when elements are anchored to the outer webs to effect the force- or form-fitting connection of an additional hollow profile bar by means of a link.
Known from U.S. Pat. No. 3,969,031 are hollow profile bars comprising sharply undercut casing grooves of small volume. The outer webs forming the casing grooves in this case are only slightly salient, but are very wide in comparison to the casing grooves. A tubular wall that is equally thick all around is present in this case as well. However, the known tubular wall forms the bottoms of the grooves, portions of their side walls and regions of the outer web. The inner circumference of the hollow profile bar is therefore corrugated, and this corrugation causes the known tubular wall to exhibit instabilities when subjected to relatively high loads by hollow profile bars that are to be clamped thereon.
The object of the invention is, therefore, to improve a hollow profile bar having the features recited in the introduction hereto in such fashion that, despite possessing a tubular wall that is equally thick all around and thus is advantageously thin, it permits the stable clamped attachment of one hollow profile bar or additional hollow profile bars, particularly when plural hollow profile bars are to be coupled thereto within the same coupling plane.
This object is achieved by the fact that slope lines of the side walls of an outer web intersect between said outer web and the axis of the bar.
It is of significance for the invention that the slope lines of the side walls of an outer web, specifically of the same outer web, intersect between said outer web and the axis of the bar. The side walls thus are much more sharply inclined, and the undercuts correspondingly greater, than when the slope lines pass through the axis of the bar or embrace it without a prior point of intersection. In no case are the slope lines perpendicular to the outer circumference of the tubular wall, but instead form an acute angle therewith. The acute angularity makes it possible for a link of a to-be-coupled hollow profile bar to engage one of the two side walls of an outer web in a radially form-fitting manner. It is of importance in this regard that the coupling sites furnished by the outer webs are close to the tubular wall, thus eliminating the possibility of any especially high lever arms on the outer webs that might lead to deformation of the outer webs and/or the tubular wall. Due to the considerable slope of the side walls of the outer webs, links coupling profile bars are able to engage only a few outer webs, or in the extreme case, only one. The links therefore take up only a small portion of the outer circumference of the tubular wall.
The hollow profile bar can be improved in such a way that the slope lines of the side walls of an outer web have a point of intersection within the tubular wall. Such an embodiment is especially advantageous when the width of the outer webs at the outer circumference of the tubular wall is approximately equal to the thickness of said wall. The resulting structure in the area of interconnection between the outer web and the tubular wall is economical of material but still sufficiently strong.
To reduce notch stresses caused by loading of the outer web in the aforesaid area of interconnection between the outer web and the tubular wall and to avoid compromising the handling of the hollow profile bar by undesirable sharp edges during coupling and during the use of the finished structure, the hollow profile bar is configured so that the side walls of an outer web transition at predetermined radii to the outer circumference of the tubular wall and/or to a visible surface of the outer web that is practically parallel to the outer wall or is arched convexly with respect thereto.
It can further be advantageous if the smallest spacing between two outer webs is practically equal to or is greater than the outer circumferential length of one of said outer webs. This results in large widths for the grooves, especially in the area of the opening thereof. It is therefore possible to use links that are of comparatively broad construction in the circumferential direction of the tube. The links can be implemented with correspondingly sturdy cross sections.
If the hollow profile bar needs to be especially sturdy in the region where it is to be engaged by links for other hollow profile bars; it can be advantageous to configure the hollow profile bar in such a way that the outer circumferential length of an outer web is practically three times the smallest spacing between two outer webs. The tubular wall then has an especially massive and correspondingly sturdy cross section between two casing grooves. Such a cross-sectional configuration of the hollow profile bar can be integrated equally successfully into an otherwise differently realized cross-sectional configuration.
The hollow profile bar is advantageously configured so that the pitch of the outer webs on tubular walls having a circularly cylindrical cross section is 22.5 or 45 angular degrees. Given that the cross sections of hollow profile bars are normally dimensioned in the range of a few centimeters, this yields an outer circumferential shape that makes it possible to work with links for to-be-connected hollow profile bars that have normal cross sections with respect to strength requirements.
A significant improvement of a hollow profile bar can be considered to reside in providing an inner wall of a tubular wall having an equal thickness all around with more than two radially salient inner webs evenly distributed about the inner circumference of said inner wall. Such inner webs can assume multiple functions. One such function is to stabilize the hollow profile bar against bowing under load. In addition, it is possible to apply links to them that engage in an end of the hollow profile bar and are able to clamp onto the inner webs. In such cases, the inner webs must protrude only as far as is necessary for them to be gripped securely by the links. They do not need to span the entire interior space of the tube, creating uninterrupted transverse walls.
In a particular manner, the hollow profile bar can be realized so that the inner webs are aligned with the undercut casing grooves. In this case, the inner webs stiffen the inner webs of the tubular wall in a region between the two outer webs, particularly against inward collapse of the inner wall. This is especially advantageous when the links are applied across two outer webs that include a casing groove between them, thus subjecting the region of the tubular wall between the outer webs to particularly high stress.
The hollow profile bar can be configured so that the pitch of the inner webs is the same as or twice that of the casing grooves. If the pitch of the inner webs is the same as that of the casing grooves, the result is ideal stiffening of the tubular wall over its entire circumference, especially if inner webs are aligned with the undercut casing grooves. Doubling the pitch of the inner webs is indicated when hollow profile bars of comparatively small cross section are to be used with the most massive possible links to clamp inner webs inside the hollow profile bar.
It is possible to configure the hollow profile bar so that each inner web comprises a broad base and a thinner clamping strip extending radially therefrom. The broad base and the thinner clamping strip placed thereon form a shoulder. The broad base is sturdier than the clamping strip, thus enabling it to safely transfer any fastening forces or other external forces exerted on the clamping strip by the structure. Broad-based inner webs are especially advantageous when they stiffen the tubular wall in the area between two outer webs.